High impedance fluid amplifier



July 15, 1969 a. E. LIGHTNER HIGH IMPEDANCE FLUID' 'AMPLIFIER Filed April 29. 1966 4 Sheets-Sheet 1 FIG.2

PRIMARY FLOW INVENTOR GENE E. LIGHTNER CONROL PRESSURE FIG."|

ATTORNEY July 15, 1969 G. E. LIGHTNER HIGH IMPEDANCE FLUID-AMPLIFIER 4 Sheets-Sheet 2 Filed April 29, 1966 FIG. 4

GENE E. LIGHTNER INVENTOR ATTORNEY y 15, 1969 G. E. LIGHTNER 3,455,325

HIGH IMPEDANCE FLUID AMPLIFIER- Filed April 2 9, 1966 4 Sheets-Sheet 3 FIG. 6

LOAD o RESISTANCE 1 figgg ffg FIG. 8

FLOW RATE INVENTOR PRESSURE CHANGE GENE E. LIGHTNER ATTORNEY July 15, 1969 s. E. LIGHTNER HIGH IMPEDANCE FLUID @MPLIFIER 4 Sheets-Sheet 4 Filed April 29, 1966 QMN ZIKOZ mode wmDwmumm 0 3m av .93 umammuE m2 0 Q INVENTOR GENE E LIGHTNER W W ATTORNEY United States Patent 3,455,325 HIGH IMPEDANCE FLUID AMPLIFIER Gene E. Lightner, St. Louis, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Apr. 29, 1966, Ser. No. 546,234 Int. Cl. F16k 9/00; F161 55/24; B01d 47/02 US. Cl. 137253 8 Claims ABSTRACT OF THE DISCLOSURE A fluid amplifier which includes an 'outer housing and a porous disc which serves as a gate forming means internally disposed in said housing. The disc divides the housing into a fluid receiving chamber and a fluid discharge chamber. A primary fluid inlet containing a gaseous fluid is introduced into the fluid receiving chamber. A secondary fluid inlet containing a control fluid is also introduced into the fluid receiving chamber. A discharge duct is connected to the discharge chamber. Thus, by controlling the pressure imposed upon the secondary fluid, the amount of surface of the disc is controlled with respect to the primary fluid passing through the disc. Thus, the primary fluid is controlled by regulating the control pressure. A number of fluid amplifiers can be connected in cascading relationship in order to amplify a primary signal. A fluid diode and a fluid amplifier having a pair of secondary fluid inlets is also disclosed.

This invention relates in general to certain new and useful improvements in fluid control devices and more particularly to high impedance fluid amplifiers which are capable of converting either pressure or mechanical motion to a pneumatic pressure or flow signal.

Fluid amplifiers which have no moving parts except for the fluid itself have been finding widespread use in a wide variety of applications where electronic components have previously been employed. There are a num ber of commercially available types of fluid amplifiers such as the stream interaction or momentum interchange type, where a power nozzle is supplied with pressurized fluid and issues a power jet or stream. A control nozzle directs the fluid against the side of the power jet and deflects the power jet away from the control nozzle. In this manner, it is possible to direct a high powered jet toward or away from a target area in response to a control stream of substantially lower power.

Another type of fluid amplifier commonly employed is the so-called boundary layer fluid amplifier where a high energy power jet is directed toward a target area by pressure distribution in a power jet boundary layer region. The pressure distribution is controlled by wall configuration. The device is designed so that the jet will lock onto one side wall in the boundary layer region and remain in the locked-on configuration even without control fluid flow.

Each of the amplifiers heretofore provided required a moving control stream. In other words, the control stream itself had to exert some moving force on the power stream in order to obtain amplification characteristics. Because of the nature of this type of device, it has been almost ice impossible to scientifically design fluid amplifiers. The interactions of the fluid circuit elements where two or more streams of moving fluids are combined makes fluid circuit design extremely difficult. Accordingly, the amplifiers heretofore provided were mainly fabricated by so-called cut-and-try methods.

It is, therefore, the primary object of the present invention to provide a fluid amplifier which is capable of being operated from a fluid supplied under pressure thereby avoiding interactions of fluid circuit elements.

It is another object of the present invention to provide a fluid amplifier of the type stated where the input impedance is reactive and is essentially infinite at steady state.

It is a further object of the present invention to provide a fluid amplifier of the type stated which has linear operating characteristics and, therefore, may be used as an analog multiplier or divider.

It is an additional object of the present invention to provide a fluid amplifier of the type stated which has no moving mechanical parts and employs a porous media and liquid level as a variable fluid resistance.

It is yet another object of the present invention to provide a method of constructing fluid amplifiers of the type stated, which method can be performed in a small amount of time at low cost and is capable of producing economically manufactured fluid amplifiers.

It is another salient object of the present invention to provide a fluid diode which operates on the principle of the fluid amplifier.

With the above and other objects in view, my invention resides in the novel features of form, construction, arrangement and combination of parts presently described and pointed out in the claims.

In the accompanying drawings:

FIGURE 1 is a schematic view partially broken away and in section of a series of fluid amplifiers constructed in accordance with and embodying the present invention and which are illustrated in a series cascading relationship;

FIGURE 2 is a schematic side elevational view partially broken away and in section of a modified form of fluid amplifier constructed in accordance with and embodying the present invention;

FIGURE 3 is an exploded perspective view showing the details of construction of the fluid amplifiers of FIG- URE 1 and the method of assembly thereof;

FIGURE 4 is a vertical sectional view showing in side elvation the fluid amplifier constructed in accordance with method of FIGURE 3;

FIGURE 5 is a schematic side elevational view, partially broken away and in section of another modified form of fluid amplifier constructed in accordance with and embodying the present invention;

FIGURE 6 is a schematic side elevational view, partially broken away and in section of a fluid diode constructed in accordance with and embodying the present invention;

FIGURE 7 is a graphical illustration of the amplification characteristics of the fluid amplifier of the present invention showing the air flow rate as a function of air pressure drop;

FIGURE 8 is a graphical illustration of a one-stage amplifier Showing the effect of a load line on pressure gain; and

FIGURE 9 is a graphical illustration showing the air flow rate through a fluid diode forming part of the present invention as a function of a normalized pressure drop.

GENERAL DESCRIPTION Generally speaking, the fluid amplifiers of the present invention comprise an outer housing which is subdivided into two chambers by means of a porous gate-forming material. Connected to the first chamber is a primary fluid inlet providing the fluid which is to be controlled and is generally a gaseous fluid. A secondary fluid input is also connected to the first chamber for supplying an input signal which serves as the control pressure and which acts upon a U-tube column of fluid. The control pressure is often referred to as the gate pressure, control pressure or gate signal which is the equivalent of the electrical analog. Fluctuations in the gate pressure cause the secondary fluid level to rise or fall, thereby decreasing or increasing the area of the porous gateforming material open to the primary air flow. The primary fluid such as the air will freely flow through the porous sheet whereas the secondary fluid does not.

A series of the above-described fluid amplifiers can be connected as schematically illustrated in FIGURE 1 so that the output signal of one fluid amplifier is connected to the primary input of the next fluid amplifier, thereby substantially increasing total amplification.

The present invention provides a modified form of fluid amplifier which is similar to the previously described type but employs two or more secondary fluid inputs which may be connected to the same control pressure source or different control pressure sources. This type of amplifier readily lends itself for use with pneumatic controllers and also serves as a pneumatic summer or pneumatic totalizer since it is capable of comparing two variable signals.

The present invention also provides a unique method of making fluid amplifiers of the type described which include assembling in marginal registration, an end plate, a secondary input manifold, a duct plate, a primary fluid input manifold, a spacer plate, a gate sheet which is fitted within a gate frame, an output manifold, and another end plate. Each of these aforementioned elements is secured in marginal registration by means of bolts or other conventional means of fastening. The primary fluid input manifold and the outlet manifold are each provided with large central apertures thereby forming chambers for receiving the fluids. Furthermore, each of these elements is provided with slots leading into each of the central chambers and the slots are conveniently fitted with fluid ports or line connectors. In similar manner, the secondary input manifold is provided with an elongated slot leading to a duct in the duct plate and which, in turn, communicates with the chamber formed in the primary input manifold.

The present invention further provides another modified form of fluid amplifier which does not employ a semiporous or porous member as a gate-forming plug. This modified form of device uses an air gap, the size of which is variable and controlled by the level of the secondary fluid in the housing. A control pressure signal impressed across the secondary fluid will thereby regulate the size of the gap and the amount of primary fluid flow therethrough.

The present invention also provides a fluid operated diode which operates on the principle of the fluid amplifier previously described. However in the case of the fluid amplifier, the secondary fluid level is maintained at a point where the entire surface of the porous gate-forming material is closed to the primary air flow. Thus after sufficient pressure in the primary fluid or primary air flow is maintained, this pressure will force the secondary fluid downwardly in the first chamber, thereby exposing a portion of the porous gate-forming material to the primary air flow. Furthermore, it can be seen that backward flow, that is flow in the opposite direction through the gate-forming material cannot occur since this flow is not capable of moving the secondary fluid.

DETAILED DESCRIPTION Referring now in more detail and by reference char acters to the drawings which illustrate a preferred embodiment of the present invention, a series of cascading fluid amplifiers is schematically illustrated in FIGURE 1. One of these fluid amplifiers A is described in detail herein and all other amplifiers in the cascading series are substantially identical thereto.

The amplifier A as schematically illustrated in FIG- URE 1 includes an outer housing 1 formed of any suitable metal such as aluminum or stainless steel or any available plastic or synthetic resin material and is subdivided into a supply chamber 2 and a discharge chamber 3 by means of a porous plate 4, which serves as a gate. The plate 4 is preferably formed of a sintered stainless steel of 0.5 to 2.0 micron diameter pores. Ceramics such as silica, alumina, chromium or other refractory oxides, etc. may also be eflectively employed as the gate-forming plate 4. Moreover, polymers such as sintered Teflon, polyolefins, vinyls, etc. and copolymers such as nylons etc. may also be employed as the plate 4.

A primary fluid input 5 is connected to the housing 1 and communicates with the supply chamber 2 for delivering a primary fluid such as air to the chamber 2. A secondary fluid input 6 is also connected to the housing 1 and communicates with the supply chamber 2 for delivering a secondary fluid to the chamber 2. The secondary fluid, which is preferably mercury, serves as the source of control pressure or gate pressure. The secondary fluid is immiscible with the primary fluid and will serve as a variable fluid resistance. The secondary fluid input 6 may be in the form of a flexible U-tube, where the bias level of the gate-forming plate 4 is adjusted by control of the U-tube leg level. Consequently, the mechanical motion, namely the movement of the U-tube level may be transmitted directly into pressure signals without hysteresis. This type of gate is unique in that it is now possible to produce desired amplifier characterisgcls according to the mathematical relationship set forth e ow.

In the operation of the device, it can be seen that the level of mercury or secondary fluid in the chamber 2 will serve as a variable fluid resistance. Where the level of mercury is high, only a small surface area of the gateforming plate 4 presents itself to the primary fluid thereby substantially reducing the amount of primary fluid passing therethrough and outwardly through a fluid outlet 7 formed in the chamber 3. Similarly, where the supply pressure is reduced, the level of mercury or secondary fluid will be reduced and the gate-forming plate 4 will present a greater surface area to the primary fluid passing therethrough. The gas flow rate through the unblocked porous media is thereby modulated by a high impedance pressure input.

The characteristics in operation of the amplifier A are analogous to the solid state field effect transistor. Transconductance of the amplifier is defined by the device geometry and the density of the fluids. The band width of the amplifier is dependent upon the column length of the secondary fluid, the volume of the output tubing and the value of the load resistance.

The basic equations which describe the fluid amplifier are set forth below.

The volume rate of flow of fluid through a porous media is given by,

q KA(AP) where K is a constant dependent on porosity of gate A is the area of flow AP is the pressure drop across the porous media X is the media thickness The area is given by,

A=hY

where: h is the height of the secondary fluid in the supply chamber measured from some .arbitrary zero,

h is given by,

(p KYAP P X (5) (oAP X e KPY (6) 3B 1,. 1 aP Pg P (7) wherein:

gm represents transconductance, r represents channel resistance, and

is the product of gm and r Other primary fluids which may be employed in the present invention are gases or vapors or liquids which are immiscible and non-reactive with the secondary fluids; such fluids are water, steam, air, oxygen, hydrogen, nitrogen, argon, neon, helium, etc. Suitable secondary fluids which may be employed in the practice of the present invention are dependent upon the interfacial tension with the gate-forming material since breakdown pressure is atfected by interfacial tension and pore diameter. Such materials are water, mercury, liquid hydrocarbons, silicone fluids, etc. However, the secondary fluid should have a high surface tension. A few suitable combinations are set forth below. However, the present invention is in no way limited to this list of usable ma- It is, of course, obvious that care must be taken when selecting these combinations. For example, a primary fluid could not be reactive with a secondary fluid. Furthermore, highly reactive materials such as chlorine are not particularly suitable. The fluid supplied to the present fluid amplifier in general can be of any type. The utilization of the term fluid encompasses any gas, liquid, semi-solid or similar type of material which can be caused to flow under the application of a pressure differential. It should also be understood that the term fluid refers to any mixture or combination of the materials that can be individually used, such as water fluid intermixed with a stream of air.

It is possible to connect the fluid outlet 7 of one fluid amplifier to the secondary fluid input 6 of another fluid amplifier A, thereby having a series of cascading fluid amplifiers as illustrated in FIGURE 1. This type of arrangement provides a much higher gain of the total system. Furthermore, the amplifier A is unique in that it is capable of converting either pressure or mechanical motion to a pneumatic pressure or a flow signal. However, a plug 8 is inserted in the output of each amplifier in a downstream position from the point where one amplifier is cascaded to the next succeeding amplifier. This plug may be formed of the same type of material as the gate forming plate 4 and is designed to permit passage of primary fluid, though in restricted quantities. The plug serves as a resistor in the same sense that a resistor would be connected to a series of cascading electrical amplifiers.

The fluid amplifier A has a long life inasmuch as only two immiscible fluids are involved and no moving parts are employed. The simple mechanical motion of the U-tube level may be transmitted directly into the control pressure. Furthermore, interactions of fluid circuit elements can be avoided by use of low impedance fluid pressure supplies. From the above, it can be seen that the fluid amplifier can be used as a process control element such as a transducer, a relay or a controller. Moreover, the fluid amplifier of the present invention may be used in either analog or digital computer circuit elements.

It can thus be seen that the fluid amplifier A operates as an isolation device where isolation may be defined as the amplification of a pressure signal from a high impedance source by means of an isolated control signal. In essence, the control signal source is not loaded down. Accordingly, the flow is created from the signal so that, in effect, an isolated signal is provided. By means of this construction, it is possible to drive many power amplifiers without distortion to the control signal. In this manner, the fluid amplifier A is substantially analogous to the electrical field effect transistor amplifier.

It is possible to provide a modified form of fluid amplifier B, substantially as schematically illustrated in FIG- URE 3 and which is similar to the previously described fluid amplifier A. The amplifier B is schematically illustrated in FIGURE 2 and also may be formed of any suitable metal such as aluminum or stainless steel or any available plastic or synthetic resinous material. The amplifier B includes an outer housing 10, which is subdivided into a supply chamber 11 and a discharge chamber 12 by means of a porous plate 13, which serves as a gate. The plate 13 is substantially similar to the plate 4 and is, therefore, not described in further detail herein. However, it should be recognized that the plate 13 may be made of the same materials as the plate 4.

A primary fluid input 14 is connected to the housing 10 and communicates with the supply chamber 11 for delivering a primary fluid such as air to the chamber 11. The primary fluid input 14 is connected to a suitable source of supply pressure (not shown). A secondary fluid input 15 is also connected to the housing 1 and communicates with the supply chamber 11 and serves as the source of control pressure or gate pressure. The primary and secondary fluids employed may be any of those fluids employed in connection with the amplifier A. The secondary fluid also serves as a variable fluid resistance. Furthermore, the secondary fluid input 15 may be in the form of a flexible U-tube where the bias level of the gate-forming plate 13 is adjusted by control of the U-tube leg level. The level of the secondary fluid in the chamber 11 determines the amount of surface area available to the flow of primary air fluid. The primary air will pass through the chamber 11 into the chamber 12 and outwardly therefrom in a fluid outlet 16. Another secondary fluid input 17 is also connected to the housing 10 in the manner as illustrated in FIGURE 2. and contains the same secondary fluid input 15. Thus, either of the secondary fluid inputs or 17 may be connected to the same control pressure source or different control pressure sources. Where the level of the secondary fluid in the chamber 11 is high, only a small area of the gate-forming plate 13 presents itself to the primary fluid thereby substantially reducing the amount of primary fluid passing therethrough. Similarly, where supply pressure is reduced, the level of the secondary fluid will be reduced and the gate-forming plate will present a greater surface area to the primary fluid passing therethrough. It should be recognized that a control pressure signal on either of the secondary inputs 15 or 17 will raise the secondary fluid level in the chamber 11. Similarly, a reduction in the supply pressure on either of the secondary fluid inlets 15 or 17 will lower the level of the secondary fluid in the chamber 11.

By means of this construction, it can be seen that the fluid amplifier B is well adapted for use with pneumatic controllers. For example, the setpoint signal of the pneu matic controller could be connected to one of the secondary fluid inputs such as the fluid input 15 and the process variable signal could be connected to the other of the secondary fluid input 17. In effect, the fluid amplifier B would thereby serve as a summer or totalizer, since it would in effect compare the process variable signal with the setpoint signal. It should also be recognized that more than two secondary fluid inputs may be employed for summation or comparison of a number of setpoint signals.

FIGURE 4 illustrates a preferred construction of the fluid amplifier of the present invention and FIGURE 3 illustrates the preferred method of making the fluid amplifier. The amplifier A is generally rectangular and includes a series of components stacked in marginal registration. The amplifier A comprises a pair of end plates 20, 21 and disposed next to the end plate is a rectangularly shaped secondary input manifold 22. The manifold 22 is provided with a secondary fluid input in the form of a plug receiving slot 23, which, in turn, merges into an elongated angularly located slot 23, the latter serving as a secondary fluid chamber. The slot 23 communicates with a circular duct 24 formed in a duct plate 24', the latter being disposed in facewise relation with one surface of the secondary input manifold 22. A hollow rectangular plug 25, preferably made of stainless steel, is fitted within a rectangular slot 25 formed in the lower end of the duct plate 23. The plug 25 may be secured with a suitable adhesive or by any other conventional means in the slot 25'. The central bore of the plug 25 communicates with the circular duct 24 and the secondary input manifold 22 through an aperture 26 formed in the duct plate 23, as illustrated in FIGURES 3 and 4. In this manner, fluid may be injected into or withdrawn from the secondary fluid chamber 23'. A stainless steel screw 26 is removably inserted into the base of the plug 25. A gate frame 32, which is provided with a large rectangular aperture retains a gate sheet 33 in facewise disposition against one surface of the spacer plate 30, the gate sheet 33 being the same as the gate forming plate 4. Disposed on the one flat surface of the gate frame 32 is an outlet manifold 34 having a port receiving slot 35 formed in its upper end and which, in turn, communicates with a large central fluid outlet chamber 36. Again, it can be seen that the central aperture 31 has the same size and shape as the chamber 29 and the chamber 36, in turn, has the same size and shape as the central aperture 31. Finally, the end plate 21 is facewise disposed on the outer surface of the outlet manifold 34. Each of these aforementioned elements are then secured by means of screws 37 and nuts 38 which extend through aligned apertures 39 formed in each of the aforementioned components. Finally, conventional ports p such as hollow tubes or plugs may be inserted in each of the slots 23, 28 and 35, in the manner as illustrated in FIGURE 3 to produce the finally assembled fluid amplifier of FIG- URE 4. It should be recognized that a number of fluid control elements could be mounted in a unitary package by this method. In fact, an entire fluid circuit could be constructed by the method of the present invention.

It is possible to provide another modified form of fluid amplifier C, substantially as illustrated in FIGURE 5 and which operates in a manner similar to the previously described fluid amplifier A. The fluid amplifier C includes an outer Y-shaped housing 40 which is preferably constructed of any of the materials from which the housing A is constructed, such as any of the suitable metals or plastic or synthetic resinous materials previously set forth. The housing 40 comprises a pair of spaced upwardly extending legs 41, 42, which are connected along a common margin 43 and communicatewith a secondary fluid leg 44 in the manner as illustrated in FIGURE 5. The secondary fluid leg 44 is preferably U-shaped in vertical cross section and is connected to a suitable source of control pressure (not shown). At the point of connection 43, the legs 41, 42 are formed with an inwardly extending baflie 45. A primary fluid source in the form of a supply pressure is connected to the housing 40 and communicates with a supply chamber 46 formed in the leg 41. The primary fluids and the secondary fluids are preferably those fluids which were previously described. Again, the depending leg or secondary input 44 may be in the form of a flexible U-tube where the bias level of the entire device is adjusted by control of the U-tube leg level. Accordingly, mechanical motion may also be used so that movement of the U-tube level may be transmitted directly into pressure signals without hysteresis.

The leg 42 forms a fluid receiving chamber 47 and also a fluid output. Consequently, when a secondary fluid is disposed in the secondary fluid leg 44, the upper level 48 in the chamber 46 may be slightly spaced from the lower margin of the baffle 45, thereby providing a gateforming space 49. Thus, it can be seen that the fluid amplifier C is substantially similar to the fluid amplifier 8, but employs a variable air space as the gate-forming element. Thus, where a high control signal pressure is applied to the secondary fluid leg 44, the level 48 of the secondary fluid Will rise, thereby decreasing the gateforming space 49. In similar manner, where the control pressure signal is reduced, the level 48 of secondary fluid may be reduced thereby increasing the gate-forming space 49. Accordingly, it can be seen that when the size of the gate-forming space 49 is increased, this is analogous to providing greater surface area on the gate-forming plate 4 and thereby permitting greater flow of primary fluid. In like manner, when the gate-forming space 49 is reduced, this is analogous to reducing the surface area available on the gate-forming plate 4 to the primary fluid. Accordingly, this will reduce the amount of primary fluid flow.

Consequently, the secondary fluid also provides a means for modulating the primary fluid flow through the fluid amplifier C. Again, it can be seen that the characteristics of the amplifer C is analogous to the solid-state field effect transistor. Furthermore, transconductance of the amplifier C may be defined by the device geometry and density of'the various primary and secondary fluids which may be employed. Moreover, the band width of the amplifier C is also dependent upon the column length of the secondary fluid, the volume of the output media, and a value of the load resistance.

It should be recognized that the amplifiers A, B and C may not be true fluid analogues of electric amplifiers until a resistance is connected to the output of each of thesefluid amplifiers with a by-pass connected across the resistance to effect a partial by-pass of the resistance. The resistance may be in the form of a porous plug which permits a restricted flow of the primary fluid. This is analogous to placing a load on the electrical analogue, namely the field effect transistor.

As indicated above, the fluid amplifier is capable of being used in a multitude of operations and in substantially any type of fluid network or circuit where the analogue, that is the field eflect transistor could be used in an electrical circuit or network. Furthermore, the fluid amplifier described herein readily lends itself to a wide variety of applications such as a fluid diode D.

The employment of the fluid amplifier as a fluid diode D is more fully illustrated in FIGURE 6 and generally comprises an outer housing 50 formed of any suitable metal such as aluminum or stainless steel or any available plastic or synthetic resin material and is subdivided into a supply chamber 51 and a discharge chamber 52, by means of a porous plate 53, which serves as a gate. The gate 53 is, in turn, substantially similar to the plate 4 and may be formed of the same material. A primary fluid inlet 54 is connected to the housing 50 and communicates with the supply chamber 51 and serves as the source of supply pressure or gate pressure. The secondary fluid which is again preferably mercury or another fluid which may be immiscible With the primary fluid is used as the variable fluid resistance and is admitted to the chamber 51 by means of a secondary fluid inlet 55. It is to be noted that the secondary fluid inlet 55 is connected to the bottom of the chamber 51 whereas the primary fluid inlet 54 is connected to the upper end of the chamber 51. The secondary fluid inlet 55 is in the form of a U- shaped tube and is supplied with a rather substantial quantity of secondary fluid.

By further reference to FIGURE 6, it can be seen that the secondary fluid completely fills the chamber 51 and extends upwardly into the primary fluid inlet 54. Furthermore, the same level of secondary fluid is achieved in the secondary fluid inlet 55 as in the primary fluid inlet 54 under zero gate pressure conditions. Consequently, no available surface of the gate forming plate 53 is presented to the primary inlet fluid.

In its operation, the primary inlet supply pressure must exceed the pressure maintained by the head of fluid in the primary fluid inlet 54. When this point occurs, the secondary fluid in the primary inlet 54 will be forced downwardly and additional fluid will be forced outwardly of the chamber 51. This will cause a rise of fluid in the secondary inlet 55. As this occurs, a portion of the gateforming plate 53 will be exposed to the primary inlet fluid, thereby permitting the primary inlet fluid to pass through the plate 53 and through a fluid outlet 56. A sufficient amount of primary fluid will pass through the plate 53 until the primary pressure has been decreased to a point where it does not exceed the pressure previously maintained by the head of secondary fluid in the primary inlet 54. At this point, the secondary fluid will rise to its original level as indicated in FIGURE 6. It should be recognized that the primary supply fluid cannot flow backwardly through the gate-forming plate 53 because of the head of pressure maintained by the secondary fluid in the chamber 51. In effect, it should be recognized that sufficient back pressure could be maintained so that the primary fluid would actually pass through the gate-forming plate 53 and thereby cause large bubbles which would pass through the secondary fluid. However, at this point, the maximum limit of eflicient operation of the device would have been achieved. In its operative range, however, fluid cannot pass backwardly, that is from the chamber 52 into the chamber 51 through the gate-form ing plate 53. Consequently, the fluid diode D operates in a fluid circuit in the same manner as a diode would operate in an electrical circuit.

A feedback line (not shown) may also be connected across the diode D in order to increase the useful pressure range of the device. This feedback line would be connected to the fluid outlet 56 and to the secondary input 55. Since the discharge pressure has a tendency to block flow and the primary input pressure allows flow, the useful range of operation of the diode D would be materially increased. It should also be understood that the diode as 10 illustrated in FIGURE 6 has a sufiiciently wide range of operation for most applications.

It should be recognized that the fluid amplifiers of the present invention may be connected in any of a plurality of combinations to form fluid networks. For example, the fluid amplifiers A and B of the present invention could be combined to form a differential input operational amplifier. In this type of device, two cascading amplifiers A would be connected in the manner as illustrated in FIG- URE 1. The output of an amplifier B would be connected to the secondary input of the first of said fluid amplifiers A. Furthermore, each of said amplifiers A and B would be connected to a common source of primary fluid to be controlled. Finally, the output of the last amplifier A in the cascading series would be connected to one of the secondary inputs of the amplifier B. The other of the secondary inputs of the amplifier B would be connected through any impedance such as through a capacitive or resistive type impedance to another primary fluid source. The output of this amplifier would be connected to the feedback line between the last of the cascading series of amplifiers A and the secondary input of the amplifier B. This type of fluid circuitry has proved to be highly eflicient for a differential input operational amplifier. Thus, it can be seen that a large variety of fluid networks can be constructed with the fluid control elements of the present invention.

The invention is further illustrated by, but not limited to, the following examples:

Example 1 A fluid amplifier was constructed of clear Lucite plastic. A sintered 316 stainless steel sheet having an overall thickness of and dimensions of /3" x 1 /2" was employed as the gate. This sheet had an average pore size of 2 microns diameter. Furthermore, a soft rubber gasket was used around the edge in the laminated structure forming the amplifier to prevent leaking around the edges of the gate. An air input was connected directly to the primary fluid input. A source of air pressure was also connected to the input line of a flexible mercury tube which. was, in turn, connected to the secondary fluid input of the amplifier and provided a control signal. The supply and bias pressures were adjusted by Mason-Eiland pressure regulators which were interposed Within each of the fluid input lines. Bias pressure was measured as the mercury level which was employed as the secondary fluid. Air was employed as the primary fluid as indicated. In operation, the supply pressure remained constant at the source. Fluctuations in the gate pressure caused the mercury level to rise or fall so as to decrease or increase the area of the porous sheet open to air flow.

Characteristic curves were obtained by the test circuit described above and the fluid amplifier characteristics were thus determined. The curves are illustrated in FIG- URE 7 and show the flow rate of primary fluid as a function of pressure drop for various bias levels in pounds per square inch. The air flow rate was plotted as a function of the air pressure drop for various bias pressure levels. The various values of bias pressure in terms of pounds per square inch are equal to the input pressures minus the supply pressures. The breakdown pressure P was found to be about 12 p.s.i. The breakdown pressure is the pressure at which it was found that the secondary fluid will flow through the porous stainless steel. Generally, the pressure required to cause flow of fluid through a porous media imposes a limit on the allowable pressure drop across the media. Mercury does not wet porous stainless steel. However, as pressure builds up on the mercury side, the liquid surface will begin to deform into the pores and at a critical pressure will flow therethrough. The various constant parameters are set forth in Table I, where the change in volume with respect to time is indicated for various input pressures, bias pressures and output pressures.

Hg inches Y P output, Meter turns, Time of meter above bottom dQ/dt P input, p.s.1.g. p.s.i.g. P bias, p.s.1.g. 0.1 cf./turn run, min. of gate AP'(p.s.i.) (ftfi/min.)

FIGURE 8 illustrates the effect of a load line on pressure gain in a one stage amplifier. In this figure, the air pressure change across the device was plotted as a function of mass flow rate. The lines with negative slopes are negative reciprocals of various load resistances. Consequently, the negative sloped lines represent the load lines. The positively sloped lines represent the input pressure parameters. It can thus be seen that the maximum gain is obtained when one of the load lines is perpendicular to one of the input pressure parameters. For a fixed input pressure swing, and supply pressure, pressure gain passes through a maximum at some value of load resistance. This is similar to a field effect transistor where the source impedance would be approximately equal to the load resistance at maximum gain. Consequently, from FIGURE 8, the maximum gain of the fluid amplifier can be determined from the air pressure supply and the mass rate of flow.

Example 2 This example shows the use of the fluid amplifier as a diode. The diode studied in this example employed the fluid amplifier of Example 1. Again, mercury was used as the secondary fluid and air was employed as the primary fluid. Furthermore, the gate pressure was held substantially constant. The air input was connected directly to the primary inlet and the secondary fluid inlet was a flexible tube containing mercury. The supply pressure was adjusted by a single Mason-Eiland pressure regulator which was interposed in the primary fluid input. The output of the amplifier was connected to a Brooks Type 1356 glass ball rotometer where a side reading of 10.0 equaled an air flow rate of 2 c.f.m. The output of the rotometer was a measure of the mass rate of flow, dQdt. The forward or input pressure was recorded as a function of rotometer reading, the flow and the normalized diflerential pressure in pounds per square inch. These data are plotted in Table 11 set forth below.

TABLE 11 Forward Rotometer Air flow Normalized pressure, p.s.i.g. reading rate, c.f.m. AP, p.s.i.

It was found that a bias head of mercury was equal to approximately 2.2 psi. The back pressure breaks through, that is passes through the gate-forming plate 13, when the bias head is equal to the differential pressure. At this point, air will being to bubble through the mercury.

The normalized pressure drop was plotted as a function of the air flow rate and this plot is illustrated in FIGURE 9. It can be seen that an almost substantially straight line showing a linear relationship is produced.

However, the slight curve at the lowerend of this-plot is due to the large width at the top of the gate. Ithas been found that by reducing this width at the top of 'the gate,-the curve produced is almost completely linear.

It should be understood that changes and modifications in the form, construction, arrangement and combination of parts presently described and pointed out may bernade and substituted for those herein shown without departing from the nature and principle of my invention.

Having thus described my invention, what I desire to claim and secure by Letters Patent is:

1. A cascading system of fluid control elements wherein said system comprises:

(1) a plurality of control element housings,

(2) a primary fluid in let to each such housing supplied with a fluid from a source independent of each -of said housings where the rate of primary fluid flow is to be controlled,

(3) a fluid receiving chamber in each said housing 'for receiving the fluid from said primary fluid inlet,

(4) a fluid discharge chamber in each said housing to receive the primary fluid for discharge,

(5) a fluid outlet in each said housing andcommunicating with said discharge chamber, (6) gate forming means interposed between said fluid receiving chamber and said fluid discharge chamber in each said housing, I

(7) a secondary fluid inlet opening into said fluid receiving chamber,

(8) and means connecting the fluid outlet of one such housing to the secondary fluid inlet of the next successive housing in said system of control elements for regulating the quantity of a secondary fluid'introduced into said fluid receiving chamber of eachsaid housing to vary the surface area of said gate forming means available to said primary fluid in said housing, thereby controlling the primary fluid passing through said system.

2. The cascading system of fluid control elements of claim 1 wherein the primary and secondary fluids are immiscible. i

3. The cascading system of fluid control elements of claim 1 wherein the primary fluid is a gas and the secondary fluid is a liquid. p

4. The cascading system of fluid control elements of claim 1 wherein the primary fluid isair, the secondary fluid is mercury and the gate forming means is porous sintered stainless steel. Y

5. A fluid control element comprising 1" (l) a housing,

(2) a primary fluid inlet supplied with a fluid Where the rate of flow is to be controlled, I (3) a chamber in said housing for receiving the fluid from said primary fluid inlet,

(4) a fluid outlet in said housing,

(5) gate forming means interposed chamber and said fluid outlet,

- between. said 13 14 (6) a plurality of independent secondary fluid inlets and primary fluid inlet to permit exposure of a poropening into said chamber, tion of said surface area for primary fluid flow in one (7) and means for regulating the quantity of asecond direction and to cover the entire surface area to ary fluid introduced into said chamber to vary the prevent primary fluid flow in the opposite direction. surface area of said gate forming means available 8. The fluid diode of claim 7 wherein the primary and to said primary fluid, thereby controlling the primary secondary fluids are immiscible. fluid passing said gate forming means and through said fluid outlet. References Cited 6. The fluid control element Of claim wherein the UNITED STATES PATENTS gf jf 968,677 8/1910 Moore 137 253 X (1) a housing, 2,342,303 2/1944 Safford 13846 (2) a primary fluid inlet supplied with a fluid where the 2588214 3/1952 Dawsfm 137 251 rate f fl is to be controlled, 2,711,752 6/1955 Schmldt 137253 (3) a chamber in said housing for receiving the fluid 7 10/1962 Agutter et a1 X from said p i y i l OXley et a1. X (4) a fluid outlet in said housing, FOREIGN PATENTS (5l)jelgzltleir(iilecatslinterposed between said cham- 3,618 9/1877 Great B ritai n.

43,160 12/1933 France.

(6) a secondary fluid inlet opening into said chamber,

(7) and gate pressure control means for regulating the WILLIAM F. ODEA, Primary Examiner introduction of a quantity of a secondary fluid into said chamber in an amount suflicient to cover the DENNIS LAMBERT Asslstant Exammer entire surface area of said gate forming means available to said primary fluid,

(8) means to control the gate pressure control means 138-46; 261-126 

